1. Field of the Invention
The present invention relates to a theft prevention system having a theft prevention apparatus for checking a first identification code transmitted from a portable unit such as an ignition key, a remote control key, or the like, and transmitting a second identification code through a communication line to an engine control apparatus, and an engine control apparatus for checking the second identification code transmitted through the communication line from the theft prevention apparatus and controlling the startup of an engine based on the checked second identification code.
2. Description of the Related Art
There has been known a theft prevention system, also referred to as an immobilizer system, for preventing a motor vehicle from being stolen by an unauthorized action to start the engine mounted on the motor vehicle. The theft prevention system allows the engine to be started when an ID code (referred to as a key ID code or a first identification code) is checked through communications with an ignition key incorporating a communication unit.
The theft prevention system has a theft prevention apparatus (also referred to as an immobilizer unit or an immobilizer ECU) for communicating with a key and checking a first identification code transmitted from the key, and an engine control apparatus (also referred to as an engine control module or an engine ECU) for communicating with the theft prevention apparatus and controlling the startup of the engine.
If the first identification code transmitted from the key is not checked, then the key is judged as being not a legitimate key, and the engine control apparatus cuts off the supply of fuel to the engine and prevents an igniter from igniting the fuel, thereby inhibiting the startup of the engine and hence preventing the motor vehicle from being stolen.
To prevent the engine control apparatus from permitting the engine to start easily when the theft prevention apparatus is removed from the motor vehicle, a communicating and checking process is performed between the theft prevention apparatus and the engine control apparatus, using an ID code (second identification code) which is different from the first identification code.
If the theft prevention apparatus or the engine control apparatus is replaced with a new one, then it is necessary to equalize second identification codes that are used between them.
Heretofore, when the theft prevention apparatus or the engine control apparatus is replaced with a new one, it has been customary to register a second identification code in the theft prevention apparatus or the engine control apparatus, using a dedicated tester.
However, the use has found the registering process inconvenient because the registering process can only be performed at a car dealer having a repair shop which owns the dedicated tester.
To improve convenience for users, Japanese laid-open patent publication No. 2000-108848 discloses a process of equalizing second identification codes in two ECUs, i.e., a theft prevention apparatus and an engine control apparatus, when special conditions are satisfied, e.g., a registering dedicated switch on the engine control apparatus is turned on, an ignition switch is turned on, an engine rotational speed is 0 rpm, and a vehicle speed is 0 km/h continuously for a given period of time, e.g., about 30 minutes. The disclosed process allows the user to perform the registering process simply and reliably without the need to go to a dealer owing a dedicated tester.
According to the disclosed process, however, a malicious third party may possibly prepare a portable unit and a theft prevention apparatus, whose first identification codes are identical to each other, and install the theft prevention apparatus on a motor vehicle, and make an action to satisfy the above conditions to steal the motor vehicle.
In addition, the disclosed process is still inconvenient in that even an authorized person cannot complete the registering and updating process before the above given period of time elapses.